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Knob and tube wiring



Knob and tube wiring

The first standardized wiring in buildings and home, in common use in America from about 1880 to the 1930s, was knob and tube wiring: single conductors were run through cavities between the structural members in walls and ceilings, with ceramic tubes forming protective channels through joists and ceramic knobs attached to the structural members to provide air between the wire and the lumber and to support the wires. Since air was free to circulate over the wires, smaller conductors could be used than required in cables. By arranging wires on opposite sides of building structural members, some protection was afforded against short-circuits that can be caused by driving a nail into both conductors simultaneously. Then by the 1940s, the labor cost of installing two conductors rather than one cable resulted in a decline in knob and tube installations.

Submitted by GeraldGoforth on Mon, 02/08/2010 - 16:28.

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